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Sep 23, 2013
09/13

Sep 23, 2013
by
Tim Scheffler; Dietrich E. Wolf

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The dissipation rate due to inelastic collisions between equally charged, insulating particles in a dilute granular medium is calculated. It is equal to the known dissipation rate for uncharged granular media multiplied by a Boltzmann-like factor, that originates from Coulomb interactions. We include particle correlations by introducing an effective potential, that replaces the bare Coulomb potential in the Boltzmann factor. All results are confirmed by computer simulations.

Source: http://arxiv.org/abs/cond-mat/9904171v1

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Sep 23, 2013
09/13

Sep 23, 2013
by
Ph. Boucaud; C. P. Korthals Altes

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At temperatures well above the transition, QCD admits a thermally reduced version in 3D, which reproduces the long distance physics. We analyze the phase diagram, point out the relevance of Z(3) symmetry in the location of the transition and suggest a way out to reconcile this with the data. Related to this symmetry is the existence of an observable, the Z(N) wall, or rather its 3D version, and discuss some of its advantages over other observables.

Source: http://arxiv.org/abs/hep-lat/9904006v1

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Sep 23, 2013
09/13

Sep 23, 2013
by
S. V. Zharikov; V. V. Sokolov

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The observations with the SAO-RAS 6-m telescope in July-August 1998 show that the GRB970508 optical remnant has varied very little since November 1997. We can conclude that we observe a proper host galaxy without the GRB optical remnant. The fitting results of the light curve of the GRB remnant plus the host galaxy until about 400 days after the primary event are reported here. The best $\chi^2$-fits with a power law, for most of the filters used, are not acceptable. Some intrinsic variability...

Source: http://arxiv.org/abs/astro-ph/9904160v1

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Sep 23, 2013
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Sep 23, 2013
by
Alexander Dvorsky; Siddhartha Sahi

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We construct an explicit realization of a minimal representation of G, where G is the conformal group of a real Jordan algebra N. We characterize spherical vectors for these representation and prove that they are closely related to the Bessel K-function $K_\tau (z)$. The resulting construction can be used to study tensor powers of the minimal representation and establish an extension of the Howe duality correspondence to some exceptional groups.

Source: http://arxiv.org/abs/math/9904051v1

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Sep 23, 2013
09/13

Sep 23, 2013
by
Zhe Chang

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The quantum Anti-de Sitter (AdS) group and quantum AdS space is discussed. Ways of getting the quantum AdS group from real forms of quantum orthogonal group are presented. Differential calculus on the quantum AdS space are also introduced. In particular, reality of differential calculus are given. We set up explicit relationships between quantum group and quantum algebra, which can be refereed as the quantum counterpart of the classical exponential. By this way, quantum AdS algebra is deduced...

Source: http://arxiv.org/abs/hep-th/9904091v1

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Sep 23, 2013
09/13

Sep 23, 2013
by
K. M. Leighly; J. P. Halpern; H. Awaki; M. Cappi; S. Ueno; J. Siebert

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Scanning and pointed RXTE observations of the nearby Seyfert 2 galaxy NGC 6300 reveal that it is a source of hard X-ray continuum and large equivalent width Fe K$\alpha$ emission. These properties are characteristic of Compton-reflection dominated Seyfert 2 galaxies. The continuum can be modeled as Compton-reflection; subsolar iron abundance is required and a high inclination preferred. However, the poor energy resolution of RXTE means that this description is not unique, and the continuum can...

Source: http://arxiv.org/abs/astro-ph/9904155v1

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Sep 23, 2013
09/13

Sep 23, 2013
by
M. A. R. de Cara; O. Pla; F. Guinea

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The minority model was introduced to study the competition between agents with limited information. It has the remarkable feature that, as the amount of information available increases, the collective gain made by the agents is reduced. This crowd effect arises from the fact that only a minority can profit at each moment, while all agents make their choices using the same input. We show that the properties of the model change drastically if the agents make choices based on their individual...

Source: http://arxiv.org/abs/cond-mat/9904187v1

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28

Sep 23, 2013
09/13

Sep 23, 2013
by
M. M. Sharma

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The compressibility of nuclear matter has received significant attention in the last decade and a variety of approaches have been employed to extract this fundamental property of matter. Recently, significant differences have emerged between the results of relativistic and non-relativistic calculations of breathing mode giant monopole resonance (GMR). This is due to a lack of understanding of the dynamics of GMR and of its exact relationship to the compression modulus of the infinite nuclear...

Source: http://arxiv.org/abs/nucl-th/9904036v1

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Sep 23, 2013
09/13

Sep 23, 2013
by
S. M. Bilenky; C. Giunti; W. Grimus; T. Schwetz

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It is shown that the Super-Kamiokande atmospheric up--down asymmetry, together with the results of all other neutrino oscillation experiments, allows to constraint the possible spectra of four massive neutrinos. The two schemes with two pairs of neutrinos with close masses separated by a gap of about 1 eV are favored by the data.

Source: http://arxiv.org/abs/hep-ph/9904316v1

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Sep 23, 2013
09/13

Sep 23, 2013
by
Carlo Rovelli

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We explore the relation between noncommutative geometry, in the spectral triple formulation, and quantum mechanics. To this aim, we consider a dynamical theory of a noncommutative geometry defined by a spectral triple, and study its quantization. In particular, we consider a simple model based on a finite dimensional spectral triple (A, H, D), which mimics certain aspects of the spectral formulation of general relativity. We find the physical phase space, which is the space of the onshell Dirac...

Source: http://arxiv.org/abs/gr-qc/9904029v1

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Sep 23, 2013
09/13

Sep 23, 2013
by
Stefan Boettcher; Allon G. Percus

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We describe a general-purpose method for finding high-quality solutions to hard optimization problems, inspired by self-organized critical models of co-evolution such as the Bak-Sneppen model. The method, called Extremal Optimization, successively eliminates extremely undesirable components of sub-optimal solutions, rather than ``breeding'' better components. In contrast to Genetic Algorithms which operate on an entire ``gene-pool'' of possible solutions, Extremal Optimization improves on a...

Source: http://arxiv.org/abs/math/9904056v1

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34

Sep 23, 2013
09/13

Sep 23, 2013
by
Jan Naudts

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In the case of a system with an unbounded hamiltonian the entropic index q of non-extensive thermodynamics has an upperbound q_c>1 beyond which the formalism becomes meaningless. The expression 1/(q_c-1) is the dimension of the state space (i.e. the manifold of density matrices) in the context of non-commutative geometry. For q=q_c an ultraviolet cutoff E < E_ub is needed to guarantee the existence of the equilibrium density matrix. Duality between q>1 and q 1/q transformation is...

Source: http://arxiv.org/abs/cond-mat/9904070v2

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Sep 23, 2013
09/13

Sep 23, 2013
by
P. Helbig; D. R. Marlow; R. Quast; P. N. Wilkinson; I. W. A. Browne; L. V. E. Koopmans

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We present constraints on the cosmological constant $\lambda_{0}$ from gravitational lensing statistics of the Jodrell Bank-VLA Astrometric Survey (JVAS). Although this is the largest gravitational lens survey which has been analysed, cosmological constraints are only comparable to those from optical surveys. This is due to the fact that the median source redshifts of JVAS are lower, which leads to both relatively fewer lenses in the survey and a weaker dependence on the cosmological...

Source: http://arxiv.org/abs/astro-ph/9904175v1

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Sep 23, 2013
09/13

Sep 23, 2013
by
Christopher A. Metzler; Martin White; Michael Norman; Chris Loken

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Hierarchical theories of structure formation predict that clusters of galaxies should be embedded in a web like structure, with filaments emanating from them to large distances. The amount of mass contained within such filaments near a cluster can be comparable to the collapsed mass of the cluster itself. Diffuse infalling material also contains a large amount of mass. Both these components can contribute to the cluster weak lensing signal. This ``projection bias'' is maximized if a filament...

Source: http://arxiv.org/abs/astro-ph/9904156v1

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Sep 23, 2013
09/13

Sep 23, 2013
by
Javier Burguete; Hugues Chate; Francois Daviaud; Nathalie Mukolobwiez

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We present and analyze experimental results on the dynamics of hydrothermal waves occuring in a laterally-heated fluid layer. We argue that the large-scale modulations of the waves are governed by a one-dimensional complex Ginzburg-Landau equation (CGLE). We determine quantitatively all the coefficients of this amplitude equation using the localized amplitude holes observed in the experiment, which we show to be well described as Bekki-Nozaki hole solutions of the CGLE.

Source: http://arxiv.org/abs/patt-sol/9904005v1

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Sep 23, 2013
09/13

Sep 23, 2013
by
Kavan U. Ratnatunga; Richard E. Griffiths; Eric J. Ostrander

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Quantitative morphological and structural parameters are estimated for galaxies detected in HST observations of WFPC2 survey fields. A modeling approach based on maximum likelihood has been developed for two-dimensional decomposition of faint under-sampled galaxy images into components of disk and bulge morphology. Decomposition can be achieved for images down to F814W (I) \~23.0, F606W (V) ~23.8 and F450W (B) ~23.3 magnitudes in WFPC2 exposures of one hour. We discuss details of the fitting...

Source: http://arxiv.org/abs/astro-ph/9904179v1

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38

Sep 23, 2013
09/13

Sep 23, 2013
by
A. Connes; D. Kreimer

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We discuss the prominence of Hopf algebras in recent progress in Quantum Field Theory. In particular, we will consider the Hopf algebra of renormalization, whose antipode turned out to be the key to a conceptual understanding of the subtraction procedure. We shall then describe several occurences of this or closely related Hopf algebras in other mathematical domains, such as foliations, Runge Kutta methods, iterated integrals and multiple zeta values. We emphasize the unifying role which the...

Source: http://arxiv.org/abs/hep-th/9904044v2

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Sep 23, 2013
09/13

Sep 23, 2013
by
M. Bocquet; Th. Jolicoeur

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We generalize the nonlinear sigma model treatment of quantum spin chains to cases including ferromagnetic bonds. When these bonds are strong enough, the classical ground state is no longer the standard Neel order and we present an extension of the known formalism to deal with this situation. We study the alternating ferromagnetic-antiferromagnetic spin chain introduced by Hida. The smooth crossover between decoupled dimers and the Haldane phase is semi-quantitatively reproduced. We study also a...

Source: http://arxiv.org/abs/cond-mat/9904169v1

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45

Sep 23, 2013
09/13

Sep 23, 2013
by
F. F. Assaad

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The 2D half-filled Kondo lattice model with exchange J and nearest neighbor hopping t is considered. It is shown that this model belongs to a class of Hamiltonians for which zero-temperature auxiliary field Monte Carlo methods may be efficiently applied. We compute the staggered moment, spin and quasiparticle gaps on lattice sizes up to 12 X 12. The competition between the RKKY interaction and Kondo effect leads to a continuous quantum phase transition between antiferromagnetic and spin-gaped...

Source: http://arxiv.org/abs/cond-mat/9904178v1

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25

Sep 23, 2013
09/13

Sep 23, 2013
by
Nagayoshi Ohashi; Siow Wang Lee; David J. Wilner; Masahiko Hayashi

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We have carried out observations of the starless core L1544 in the CCS (J_N=3_2-2_1) line at 9 millimeters wavelength using the BIMA array. The maps show an elongated condensation, 0.15 x 0.045 pc in size, with stronger emission at the edges. The appearance is consistent with a flattened, ringlike structure viewed at high inclination to the line of sight. The CCS molecule is likely heavily depleted in the inner part of the core. The position velocity diagram along the major axis shows a...

Source: http://arxiv.org/abs/astro-ph/9904173v1

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29

Sep 23, 2013
09/13

Sep 23, 2013
by
L. De Maria; M. Springborg

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The electronic structure of a single monatomic gold wire is presented for the first time. It has been obtained with state-of-the-art ab-initio full-potential density-functional (DFT) LMTO (linearized muffin-tin orbital) calculations taking into account relativistic effects. For stretched structures in the experimentally accessible range the conduction band is exactly half-filled, whereas the band structures are more complex for the optimized structure. By studying the total energy as a function...

Source: http://arxiv.org/abs/cond-mat/9904181v1

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39

Sep 23, 2013
09/13

Sep 23, 2013
by
Ralf Quast; Phillip Helbig

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We reanalyse optical gravitational lens surveys from the literature in order to determine relative probabilities in the $\lambda_{0}$-$\Omega_{0}$ plane, using a softened singular isothermal sphere lens model. In addition, we examine a portion of the $\lambda_{0}$-$\Omega_{0}$ plane which includes all viable cosmological models; this is vital for comparison with other cosmological tests. The results are, within the errors, consistent with those of more specialised analyses, such as those...

Source: http://arxiv.org/abs/astro-ph/9904174v1

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32

Sep 23, 2013
09/13

Sep 23, 2013
by
Drazen Adamovic

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Let $\D$ be the Lie algebra of regular differentialoperators on ${\C} \setminus \{0\}$, and ${\hD}= {\D} + {\C} C$ be the central extension of ${\D}$. Let $W_{1+\infty,-N}$ be the vertex algebra associated to the irreducible vacuum $\hD$-module with the central charge $c=-N$. We show that $W_{1+\infty,-N}$ is a subalgebra of the Heisenberg vertex algebra M(1) with $2 N$ generators, and construct 2N-dimensional family of irreducible $W_{1+\infty,-N}$-modules. Considering these modules as...

Source: http://arxiv.org/abs/math/9904057v1

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61

Sep 23, 2013
09/13

Sep 23, 2013
by
A. Echeverria-Enriquez; M. C. Munoz-Lecanda; N. Roman-Roy; C. Victoria-Monge

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In this review the foundations of Geometric Quantization are explained and discussed. In particular, we want to clarify the mathematical aspects related to the geometrical structures involved in this theory: complex line bundles, hermitian connections, real and complex polarizations, metalinear bundles and bundles of densities and half-forms. In addition, we justify all the steps followed in the geometric quantization programme, from the standpoint definition to the structures which are...

Source: http://arxiv.org/abs/math-ph/9904008v1

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46

Sep 23, 2013
09/13

Sep 23, 2013
by
Maxim Kontsevich

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This paper is dedicated to the memory of Moshe Flato, and will appear in Lett. Math. Phys. 48 (1) It became clear during last 5-6 years that the algebraic world of associative algebras (abelian categories, triangulated categories, etc) has many deep connections with the geometric world of two-dimensional surfaces. One of manifestations of this is Deligne's conjecture (1993) which says that on the cohomological Hochschild complex of any associative algebra naturally acts the operad of singular...

Source: http://arxiv.org/abs/math/9904055v1

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26

Sep 23, 2013
09/13

Sep 23, 2013
by
T. Kifune

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We postulate in the present paper that the energy-momentum relation is modified for very high energy particles to violate Lorentz invariance and the speed of photon is changed from the light velocity c. The violation effect is amplified, in a sensitive way to detection, through the modified kinematical constraints on the conservation of energy and momentum, in the absorption process of gamma-rays colliding against photons of longer wavelengths and converting into an electron-positron pair. For...

Source: http://arxiv.org/abs/astro-ph/9904164v1

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37

Sep 23, 2013
09/13

Sep 23, 2013
by
B. G. Sidharth

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The time variation of the gravitational constant G in the recently discussed large number cosmologies accounts for the galactic rotational velocity curves without invoking dark matter and also for effects like the precession of the perhelion of Mercury.

Source: http://arxiv.org/abs/physics/9904022v2

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77

Sep 23, 2013
09/13

Sep 23, 2013
by
Wayne Hu

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Upcoming weak lensing surveys on wide fields will provide the opportunity to reconstruct the structure along the line of sight tomographically by employing photometric redshift information about the source distribution. We define power-spectrum statistics, including cross correlation between redshift bins, quantify the improvement that redshift information can make in cosmological parameter estimation, and discuss ways to optimize the redshift binning. We find that within the adiabatic cold...

Source: http://arxiv.org/abs/astro-ph/9904153v1

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30

Sep 23, 2013
09/13

Sep 23, 2013
by
R. G. Roberts

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Evolution of the parton densities at NLO in $\alpha_S$ using $\tilde W^2 = Q^2 (1-z)/z$ instead of the usual $Q^2$ for the scale of the running coupling $\alpha_S$ is investigated. While this renormalisation scale change was originally proposed as the relevant one for $x \to 1$, we explore the consequences for all $x$ with this choice. While it leads to no improvement to the description of DIS data, the nature of the gluon at low $x$, low $Q^2$ is different, avoiding the need for a...

Source: http://arxiv.org/abs/hep-ph/9904317v1

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44

Sep 23, 2013
09/13

Sep 23, 2013
by
Michael R. Merrifield; Konrad Kuijken

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It has been suggested that the boxy and peanut-shaped bulges found in some edge-on galaxies are galactic bars viewed from the side. We investigate this hypothesis by presenting emission-line spectra for a sample of 10 edge-on galaxies that display a variety of bulge morphologies. To avoid potential biases in the classification of this morphology, we use an objective measure of bulge shape. Generally, bulges classified as more boxy show the more complicated kinematics characteristic of edge-on...

Source: http://arxiv.org/abs/astro-ph/9904158v1

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31

Sep 23, 2013
09/13

Sep 23, 2013
by
A. Gammal; T. Frederico; L. Tomio; Ph. Chomaz

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We study the effects of a repulsive three-body interaction on a system of trapped ultra-cold atoms in a Bose-Einstein condensed state. The corresponding $s-$wave non-linear Schr\"{o}dinger equation is solved numerically and also by a variational approach. A first-order liquid-gas phase transition is observed for the condensed state up to a critical strength of the effective three-body force.

Source: http://arxiv.org/abs/cond-mat/9904184v1

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30

Sep 23, 2013
09/13

Sep 23, 2013
by
I. Bednyakov; L. Labzowsky; G. Plunien; G. Soff; V. Karasiev

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Electroweak radiative corrections to the matrix elements $$ are calculated for highly charged hydrogenlike ions. These matrix elements constitute the basis for the description of the most parity nonconserving (PNC) processes in atomic physics. The operator ${\hat H}_{PNC}$ represents the parity nonconserving relativistic effective atomic Hamiltonian at the tree level. The deviation of these calculations from the calculations valid for the momentum transfer $q^{2}=0$ demonstrates the effect of...

Source: http://arxiv.org/abs/quant-ph/9904052v1

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35

Sep 23, 2013
09/13

Sep 23, 2013
by
Juergen Schmidhuber

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Is the universe computable? If so, it may be much cheaper in terms of information requirements to compute all computable universes instead of just ours. I apply basic concepts of Kolmogorov complexity theory to the set of possible universes, and chat about perceived and true randomness, life, generalization, and learning in a given universe.

Source: http://arxiv.org/abs/quant-ph/9904050v1

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23

Sep 23, 2013
09/13

Sep 23, 2013
by
M. Bisani; W. Selke

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The probability distribution p(l) of an atom to return to a step at distance l from the detachment site, with a random walk in between, is exactly enumerated. In particular, we study the dependence of p(l) on step roughness, presence of other reflecting or absorbing steps, interaction between steps and diffusing atom, as well as concentration of defects on the terrace neighbouring the step. Applying Monte Carlo techniques, the time evolution of equilibrium step fluctuations is computed for...

Source: http://arxiv.org/abs/cond-mat/9904175v1

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30

Sep 23, 2013
09/13

Sep 23, 2013
by
A. Aharony; O. Entin-Wohlman; Y. Imry

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We present a general scheme for finding the exact eigenstates of two electrons, with on-site repulsive potentials U_i, on I impurities in a macroscopic crystal. The model describes impurities in doped semiconductors and artificial molecules in quantum dots. For quantum dots, the energy cost for adding two electrons is bounded by the single-electron spectrum, and does not diverge when U_i approaches infinity, implying limitations on the validity of the Coulomb blockade picture. Analytic...

Source: http://arxiv.org/abs/cond-mat/9904182v1

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31

Sep 23, 2013
09/13

Sep 23, 2013
by
A. L. Chudnovskiy; S. E. Ulloa

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A two-layer system coupled via tunneling and with different carrier masses in each layer is investigated in the integer quantum Hall regime. Striking deviations of the one-layer Hall conductivity from the usual quantization are found, if resonance between Landau levels of different layers is achieved. The appearance of negative jumps in the Hall conductivity is also predicted under suitable conditions. The results obtained are robust against disorder in the system.

Source: http://arxiv.org/abs/cond-mat/9904166v1

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Sep 23, 2013
09/13

Sep 23, 2013
by
A. D. Kaminker; P. Haensel; D. G. Yakovlev

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We calculate the neutrino energy emission rate due to singlet-state pairing of protons in the neutron star cores taking into account the relativistic correction to the non-relativistic rate. The non-relativistic rate is numerically small, and the relativistic correction appears to be about 10 -- 50 times larger. It plays thus the leading role, reducing great difference between the neutrino emissions due to pairing of protons and neutrons. The results are important for simulations of neutron...

Source: http://arxiv.org/abs/astro-ph/9904166v1

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28

Sep 23, 2013
09/13

Sep 23, 2013
by
Raimar Wulkenhaar

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For our own education, we reconstruct the Hopf algebra of Connes and Moscovici obtained by the action of vector fields on a crossed product of functions by diffeomorphisms. We extend the realization of that Hopf algebra in terms of rooted trees as given by Connes and Kreimer from dimension one to arbitrary dimension of the manifold. In principle there is no modification, but in higher dimension one has to be careful with the order of cuts. The order problem leads us to speculate that in quantum...

Source: http://arxiv.org/abs/math-ph/9904009v1

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Sep 23, 2013
09/13

Sep 23, 2013
by
Andreas Burkert; Joseph Silk

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The structure of dark matter halos as predicted from cosmological models is discussed and compared with observed rotation curves of dark matter-dominated dwarf galaxies. The theoretical models predict that dark matter halos represent a one-parameter family with a universal density profile. Observations of dark matter-dominated rotation curves indeed confirm the universal structure of dark halos. They are even in excellent agreement with the expected mass-radius scaling relations for the...

Source: http://arxiv.org/abs/astro-ph/9904159v1

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Sep 23, 2013
09/13

Sep 23, 2013
by
Z. Rudy; W. Cassing; L. Jarczyk; B. Kamys; P. Kulessa; O. W. B. Schult; A. Strzalkowski

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It is shown that the mass dependence of the $\Lambda$-lifetime in heavy hypernuclei is sensitive to the ratio of neutron-induced to proton-induced non-mesonic decay rates R_n/R_p. A comparison of the experimental mass dependence of the lifetimes with the calculated ones for different values of R_n/R_p leads to the conclusion that this ratio is larger than 2 on the confidence level of 0.75. This suggests that the phenomenological $\Delta$I=1/2 rule might be violated for the nonmesonic decay of...

Source: http://arxiv.org/abs/nucl-th/9904032v2

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Sep 23, 2013
09/13

Sep 23, 2013
by
N. Markovic; C. Christiansen; A. M. Mack; W. H. Huber; A. M. Goldman

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The superconductor-insulator transition of ultrathin films of bismuth, grown on liquid helium cooled substrates, has been studied. The transition was tuned by changing both film thickness and perpendicular magnetic field. Assuming that the transition is controlled by a T=0 critical point, a finite size scaling analysis was carried out to determine the correlation length exponent v and the dynamical critical exponent z. The phase diagram and the critical resistance have been studied as a...

Source: http://arxiv.org/abs/cond-mat/9904168v1

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25

Sep 23, 2013
09/13

Sep 23, 2013
by
Matthias Neubert

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Measurements of the rates for the hadronic decays B^+- -> pi K along with the CP-averaged B^+- -> pi^+- pi^0 branching ratio can be used to bound and extract the weak phase gamma=-arg(V_ub). Using preliminary CLEO data, we obtain the bounds |gamma|>93 degrees at 1 sigma, and |gamma|>71 degrees at 90 % confidence level.

Source: http://arxiv.org/abs/hep-ph/9904321v1

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Sep 23, 2013
09/13

Sep 23, 2013
by
David H. Cobden; Jesper Nygard; Marc Bockrath; Paul L. McEuen

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We report measurements of the temperature and gate voltage dependence for individual bundles (ropes) of single-walled nanotubes. When the conductance is less than about e^2/h at room temperature, it is found to decrease as an approximate power law of temperature down to the region where Coulomb blockade sets in. The power-law exponents are consistent with those expected for electron tunneling into a Luttinger liquid. When the conductance is greater than e^2/h at room temperature, it changes...

Source: http://arxiv.org/abs/cond-mat/9904179v1

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34

Sep 23, 2013
09/13

Sep 23, 2013
by
D. Mentrup; J. Schnack; Marshall Luban

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Analytical solutions for the time-dependent autocorrelation function of the classical and quantum mechanical spin dimer with arbitrary spin are presented and compared. For large spin quantum numbers or high temperature the classical and the quantum dimer become more and more similar, yet with the major difference that the quantum autocorrelation function is periodic in time whereas the classical is not.

Source: http://arxiv.org/abs/cond-mat/9904170v1

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Sep 23, 2013
09/13

Sep 23, 2013
by
L. Srinivasa Mohan; Prabhu R. Nott; K. Kesava Rao

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A rigid-plastic Cosserat model has been used to study dense, fully developed flow of granular materials through a vertical channel. Frictional models based on the classical continuum do not predict the occurrence of shear layers, at variance with experimental observations. This feature has been attributed to the absence of a material length scale in their constitutive equations. The present model incorporates such a material length scale by treating the granular material as a Cosserat...

Source: http://arxiv.org/abs/cond-mat/9904167v1

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Sep 23, 2013
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Sep 23, 2013
by
H. J. Lee; J. H. Jung; Y. S. Lee; J. S. Ahn; T. W. Noh; K. H. Kim; S-W. Cheong

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We investigated temperature dependent optical conductivity spectra of Nd0.7Sr0.3MnO3 single crystal. We found that polishing and surface scattering effects on the Nd0.7Sr0.3MnO3 crystal surfaces could significantly distort the optical responses, especially in the mid-infrared region. However, oxygen annealing and gold normalization processes seemed to remedy the distortions. We found that the spectral weight of Nd0.7Sr0.3MnO3 in the metallic state might be composed of a Drude carrier term and a...

Source: http://arxiv.org/abs/cond-mat/9904173v1

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Sep 23, 2013
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Sep 23, 2013
by
Jerome Martin; Alain Riazuelo; Mairi Sakellariadou

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In the context of inflation, non-vacuum initial states for cosmological perturbations that possess a built in scale are studied. It is demonstrated that this assumption leads to a falsifiable class of models. The question of whether they lead to conflicts with the available observations is addressed. For this purpose, the power spectrum of the Bardeen potential operator is calculated and compared with the CMBR anisotropies measurements and the redshift surveys of galaxies and clusters of...

Source: http://arxiv.org/abs/astro-ph/9904167v1

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Sep 23, 2013
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Sep 23, 2013
by
Wang Hui; Sa Ben-Hao; Tai An; Sun Zu-Xun

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A hadron and string cascade model, JPCIAE, which is based on LUND string model, PYTHIA event generator especially, is used to study both inclusive photon production and direct photon production in 200A GeV S + Au central collisions. The model takes into account the photon production from the partonic QCD scattering process, the hadronic final-state interaction, and the hadronic decay and deals with them consistently. The results of JPCIAE model reproduce successfully both the WA93 data of low...

Source: http://arxiv.org/abs/nucl-th/9904035v1

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Sep 23, 2013
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Sep 23, 2013
by
M. Bastero-Gil; S. F. King; J. Sanderson

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We study preheating in a general class of supersymmetric hybrid inflation model. Supersymmetry leads to only one coupling constant in the potential and thus only one natural frequency of oscillation for the homogeneous fields, whose classical evolution consequently differs from that of a general (non-supersymmetric) hybrid model. We emphasise the importance of mixing effects in these models which can significantly change the rate of production of particles. We perform a general study of the...

Source: http://arxiv.org/abs/hep-ph/9904315v1

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Sep 23, 2013
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Sep 23, 2013
by
Markus Porto; Shlomo Havlin; H. Eduardo Roman; Armin Bunde

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We consider the mean distribution functions Phi(r|l), Phi(B)(r|l), and Phi(S)(r|l), giving the probability that two sites on the incipient percolation cluster, on its backbone and on its skeleton, respectively, connected by a shortest path of length l are separated by an Euclidean distance r. Following a scaling argument due to de Gennes for self-avoiding walks, we derive analytical expressions for the exponents g1=df+dmin-d and g1B=g1S-3dmin-d, which determine the scaling behavior of the...

Source: http://arxiv.org/abs/cond-mat/9904177v1